The mechanisms by which viruses cause pathological changes in the cells they infect is an area of active current interest. In the case of vesicular stomatitis virus (VSV), the prototype rhabdovirus, a viral structural protein, the matrix (M) protein, appears to be responsible for several of the major cytopathic effects of virus infection. M protein has the ability to inhibit host-directed gene expression and to cause the characteristic rounding of VSV-infected cells when expressed in the absence of other viral components. The goal of this project is to determine the mechanism of VSV-induced cytopathic effects and to identify strategies for enhancing the resistance of host cells to the cytopathic effects of virus infection. The experiments proposed here are focused primarily on the mechanism by which VSV inhibits host- directed transcription and involve the following Specific Aims: Aim 1 is to determine the mechanism of inhibition of transcription initiation by nuclear extracts from VSV-infected cells. Our recent data indicate that virus-induced inhibition of transcription by host RNA polymerase II involves defective activity of basal transcription initiation factors and that recombinant TATA-binding protein (TBP) subunit of transcription factor IID (TFIID) can overcome the defect in nuclear extracts from VSV- infected cells. How TBP in inactivated will be determined by analysis of TBP expression and activity of TFIID purified from nuclear extracts from VSV-infected cells. We will also determine whether overexpression of TBP in vivo make cells resistant to the inhibition of host transcription by VSV. Aim 2 is to determine whether viral components other than M protein are involved in the inhibition of transcription in VSV-infected cells. This hypothesis will be tested by generating a VSV deletion mutant lacking an M gene and testing its effects on host gene expression. Upon completion of these experiments we will have identified molecular targets involved in the inhibition of host transcription by VSV, and we will have a more complete view of the viral components involved in the inhibition. These experiments should also point the way to strategies for making cells resistant to the cytopathic effects of virus infection, either by overexpressing transcription factor(s) involved in the inhibition or by genetically engineering transcription factors that are resistant to the inhibitory effects of virus infection. Cells that are resistant to one or more cytopathic effects of virus infection will constitute a valuable tool in future studies of viral pathogenesis and may also be of practical value in developing antiviral strategies in the intact host.